Long before there was “fake news,” there was the assassination of President John F. Kennedy and the scores of conspiracy theories it ignited. One author estimated that conspiracy theorists have accused “42 groups, 82 assassins, and 214 people by name of being involved in the assassination.” According to a 2013 poll, no less than 62 percent of Americans believe there was a broader plot beyond just Lee Harvey Oswald on the sixth floor overlooking Dealey plaza in Dallas.

On Thursday, President Trump released 2,800 secret assassination files from the final batch held by the National Archives. But he also withheld thousands of pages of the most sensitive documents for at least another six months, after intense lobbying by the CIA, FBI and other agencies.

JFK Files are being carefully released. In the end there will be great transparency. It is my hope to get just about everything to public!

His decision disappointed historians and conspiracy theorists alike. Even so, thousands of people began combing through the files that were put online Thursday night, including more than a dozen Post editors and reporters. What they found were documents about spies and assassination plots that spanned decades and continents.

Will the files add any fuel to the conspiracy theories that have been burning for more than half a century, or deprive them of oxygen once and for all?

Here are a few of the most prevalent conspiracy theories on the assassination.

Multiple Gunmen

Perhaps the most enduring conspiracy theory owes its origins not to some crank in a tinfoil hat but rather to the U.S. House of Representatives.

A week after Kennedy’s assassination on November 22, 1963, newly sworn-in President Lyndon B. Johnson issued an executive order creating the President’s Commission on the Assassination of President Kennedy — the Warren Commission, named after its chairman, Supreme Court Chief Justice Earl Warren.

Ten months later, the commission presented its findings: Oswald acted alone as did Jack Ruby, the Dallas nightclub owner who shot Oswald two days after Kennedy’s assassination.

In 1976 — after Watergate shook Americans’ faith in government, and after the emergence of the Zapruder film allowed the public to see the assassination for themselves — the House voted overwhelmingly to establish a Select Committee on Assassinations to reinvestigate the killing, as well as that of Martin Luther King Jr., in 1968.

Like the Warren Commission, the House investigation found no evidence of Soviet, Cuban or CIA involvement in Kennedy’s assassination. But the committee did conclude that there was “probably” a conspiracy involving a second gunman on the now infamous “grassy knoll.”

This “great contradiction,” as one JFK scholar put it, created room for conspiracy theories to grow.

Umbrella Man

The most famous theory involving multiple gunmen centers on “Umbrella Man”: a figure seen mysteriously holding a black umbrella on the sunny day of Kennedy’s assassination. Some speculated that Umbrella Man had shot a poison dart into Kennedy’s neck, immobilizing him to allow for Oswald or others to deliver a kill-shot.

The reality, however, was banal. In 1978, 15 years after the assassination, Louie Steven Witt told the House committee that he brought the umbrella to heckle — not murder — the president.

Louis Steven Witt, right, a Dallas life insurance salesman appears before the House Assassinations Committee in Washington, Sept. 25, 1978. Witt stated to the committee that he was at the scene of President Kennedy’s assassination in Dallas to heckle the President, not to signal a second assassin. The woman at the left demonstrating the umbrella is staff assistant Cyndi Cooper. (AP Photo/John Duricka)

“Has exhibit 405 ever contained a gun or weapon of any sort?” Robert Genzman, staff counsel to the committee, asked him as the committee compared Witt’s umbrella to conspiracy theorists’ diagrams of secret dart- or bullet-firing mechanisms.

“This umbrella?” replied a befuddled Witt.

“Yes.”

“No.”

Witt said he wasn’t even aware of the conspiracy theories over his umbrella until years later, and that it was “bad joke” aimed at Kennedy’s father that had monumentally backfired. (A black umbrella had been the trademark of Nazi-appeasing British Prime Minister Neville Chamberlain, whom Joseph Kennedy had supported.)

“Umbrella Man,” a 2011 short documentary by filmmaker Errol Morris, explored how, under a microscope, the innocuous could appear sinister.

“If the ‘Guinness Book of World Records’ had a category for people doing the wrong thing at the wrong time in the wrong place, I would be No. 1 in that position,” Witt told the committee, “with not even a close runner-up.”

An Inside Job

Another persistent belief is that American officials were somehow involved. One theory is that the fatal bullet actually came from the driver of Kennedy’s own car as he attempted to fire upon Oswald.

“If you look at a really bad copy of the Zapruder film, it will look like William Greer, the driver, reached over his shoulder with a gun and shot Kennedy in the head,” John McAdams, author of “JFK Assassination Logic: How to Think about Claims of Conspiracy,” told The Daily Beast. “But his hands were on the steering wheel the whole time, it only looks differently in a very bad copy of the Zapruder film.”

A more widespread conspiracy theory is that the CIA — and even Lyndon B. Johnson — were nefariously involved.

Lyndon B. Johnson is sworn in as president aboard Air Force One on Nov. 22, 1963, as his wife, Lady Bird Johnson, and a stunned Jacqueline Kennedy look on. (Cecil Stoughton/White House)

Although experts have rejected it as “ridiculous” and “contrived,” the conspiracy theory was nonetheless central to Oliver Stone’s film. It has also been pushed by another Stone: Roger Stone, the political consultant and Trump confidant who lobbied the president to release the final documents.

“I realize that delving into the world of assassination research and a belief in a conspiracy will lead some to brand me as an extremist or a nut, but the facts I have uncovered are so compelling that I must make the case that Lyndon Baines Johnson had John Fitzgerald Kennedy murdered in Dallas to become president himself and to avert the precipitous political and legal fall that was about to beset him,” Stone wrote in his 2013 book, written with Mike Colapietro, “The Man Who Killed Kennedy: The Case Against LBJ.”

(The book, which accuses Johnson of complicity in at least six other murders, also quotes Richard Nixon — Stone’s former boss — as saying “Lyndon and I both wanted to be President, the difference was I wouldn’t kill for it.”)

Sean Cunningham, a history professor at Texas Tech, said no evidence supported the theory.

Of all the conspiracy theories surrounding Kennedy’s murder, there is one that is most likely to be boosted or debunked by the newly disclosed records.

As reported by The Washington Post’s Ian Shapira, experts believe many of the 3,100 previously unreleased files relate to Oswald’s six-day trip to Mexico City two months before the assassination. Some believe Oswald received his orders from Soviet or Cuban agents while in Mexico City.

Lee Harvey Oswald is led down a corridor of the Dallas police station for another round of questioning after Kennedy’s assassination. Oswald, who denied any involvement in the shooting, was formally charged with murder. (AP Photo)

Oswald had moved to the Soviet Union in 1959, spending two and a half years there before returning to the United States when his minor celebrity as an American defector faded. In September of 1963, he traveled to the Mexican capital, visiting both the Cuban and Soviet embassies in apparent attempt to move to one of the communist countries.

“One Soviet official whom Oswald purportedly contacted, Valeriy Kostikov, was not only a KGB officer but also was believed to have worked for the KGB’s Department 13, which the CIA report described as ‘the department charged with sabotage and assassination,'” The Post reported in 1993, when a previous round of documents were declassified.

That has left historians keen to know what the last batch of records will reveal about Oswald’s movements and meetings in Mexico City.

“I’ve always considered the Mexico City trip the hidden chapter of the assassination. A lot of histories gloss right past this period,” Philip Shenon, a former New York Times reporter and the author of a book on the Warren Commission, told Shapira. “Oswald was meeting with Soviet spies and Cuban spies, and the CIA and FBI had him under aggressive surveillance. Didn’t the FBI and CIA have plenty of evidence that he was a threat before the assassination? If they had acted on that evidence, maybe it wouldn’t have taken place. These agencies could be afraid that if the documents all get released, their incompetence and bungling could be exposed. They knew about the danger of Oswald, but didn’t alert Washington.”

According to some conspiracy theories, American intelligence agencies knew of Oswald’s plot and allowed it to happen because they wanted Kennedy out of the way.

The CIA and the FBI investigated supposed Cuban and Soviet involvement but found nothing. The Warren commission and the House Select Committee on Assassinations also both ruled out Cuban or Soviet involvement. Experts have also cast doubt on a Cuban or Soviet plot, pointing to the fact that both countries considered Kennedy easier to work with than his vice president.

According to one conspiracy theory, when Oswald moved to the Soviet Union, the KGB trained a look-alike who assumed his identity and, eventually, killed Kennedy. The man behind the theory even convinced Oswald’s widow to allow him to unearth the corpse.

On Oct. 4, 1981, an exhumation team in Fort Worth, grimly discovered that Oswald’s concrete vault had cracked and that the body was badly decomposed, but enough remained inside the dark brown suit for authorities to analyze.

“We, both individually and as a team, have concluded beyond any doubt, and I mean beyond any doubt, that the individual buried under the name Lee Harvey Oswald in Rose Hill Cemetery is, in fact, Lee Harvey Oswald,” announced Assistant Dallas County Medical Examiner Linda E. Norton.

The Mob

In the days after his brother’s assassination, Robert Kennedy had a horrible feeling that the killing was his fault.

“Robert Kennedy had a fear that he had somehow gotten his own brother killed,” according to biographer Evan Thomas. “That Robert Kennedy’s attempts to prosecute the mob and to kill Castro had backfired in some terrible way, had blown back, as the intelligence folks say.”

Jackie Kennedy and her children, Caroline and John Jr., leave the Capitol, followed by Attorney General Robert F. Kennedy and his sister Patricia Kennedy Lawford on Nov. 24, 1963.

There is no public evidence of an organized crime plot against the president, however, and experts again discount the idea.

Ralph Salerno, a former New York City Police detective who investigated mafia involvement in the assassination for the House committee, said he reviewed “thousands of pages of electronic surveillances of organized crime leaders all over the United States” at the time of the assassination and heard nothing suspicious.

“We even came across a few sympathetic remarks about the president,” he told ABC. “‘No, they killed the wrong one.’ ‘They should have shot his brother.’ ‘That little SOB.’ ‘He’s the guy who’s giving us a hard time.’”

Ted Cruz’s dad

Not one to shy away from conspiracy theories, then-candidate Trump himself had a hot take on the assassination he delivered to Fox News last year.

Trump, who was at the time battling Sen. Ted Cruz (R-Texas) for the Republican presidential nomination, claimed that his opponent’s father, Rafael Cruz, had been spotted with Oswald before the shooting.

On Nov. 6, 2012, Republican Ted Cruz celebrated his election to the U.S. Senate with his father, Rafael Cruz, right, at a party in Houston. (David J. Phillip/AP)

“His father was with Lee Harvey Oswald prior to Oswald being, you know, shot,” Trump said during a telephone interview. “I mean the whole thing is ridiculous. What is this? Right? Prior to his being shot. And nobody even brings it up. I mean, they don’t even talk about that — that was reported. And nobody talks about it.”

Trump appeared to be referencing an April 2016 National Enquirer article headlined “Ted Cruz Father Linked to JFK Assassination!” The story contained a photo that, according to the tabloid, showed Oswald and Rafael Cruz distributing pro-Castro leaflets in New Orleans in 1963.

“All I did is point out the fact that on the cover of the National Enquirer, there’s a picture of him [Rafael Cruz] and crazy Lee Harvey Oswald having breakfast,” Trump said. “I had nothing to do with it. This was a magazine that frankly in many respects, should be very respected. They got O.J. They got [John] Edwards. They got this. I mean, if that was the New York Times, they would have gotten Pulitzer prizes for their reporting.”